The present invention relates to a multi-level cell copyback method in a non-volatile memory device.
In a common non-volatile memory device, one string is made up of a plurality of memory cells, and a memory cell array includes a plurality of strings.
A common method of driving the memory cell operates in accordance with level of a threshold voltage having two states. Here, a first state corresponding to one of a program area and an erase area means the level of the threshold voltage in case that the level of the threshold voltage is higher than a given level, and a second state corresponding to the other area indicates the level of the threshold voltage in case that the level of the threshold voltage is smaller than the given level.
For example, a memory cell is programmed or erased in accordance with level of a threshold voltage having a first state and a second state, wherein the first state corresponds to a level of the threshold voltage smaller than a reference voltage, i.e. 0V and the second state corresponds to the level of the threshold voltage higher than 0V. This memory cell is referred to as a single level cell (hereinafter, referred to as “SLC”). Here, since the SLC considers only two states on the basis of the reference voltage, the SLC may store accurately data. However, the SLC is not good to process mass storage data.
To improve this demerit of the SLC, a multi-level cell (hereinafter, referred to as “MLC”) has been developed.
The MLC has the same structure as the SLC in physical view. However, the MLC has at least four threshold voltage levels in logical view. That is, the threshold voltage is divided as a program area and an erase area based on a reference voltage like the SLC, but at least three threshold voltage levels exist in the program area unlike the SLC. As a result, since the MLC drives at least four states with the same physical structure as the SLC, the MLC has excellent data processing capacity compared to the SLC.
In other words, the non-volatile memory device having the MLC uses a method of storing two data in one memory cell. As a result, a method of driving the non-volatile memory device in accordance with threshold voltage distribution and bias condition of the MLC is complicated compared to a method of driving the non-volatile memory device having the SLC.
A copyback operation of the method means an operation of transferring data stored in a first memory cell into a second memory cell having different address from the first memory cell.
If algorithm for the copyback operation is existed, data in a memory cell are sensed by using a page buffer, and then are read to a device in outside of a chip. Subsequently, the read data are stored in the device, and then the stored data should be again stored in a memory cell.
In addition, in case that the non-volatile memory device does not have extra storage section except a page buffer in the chip, the stored data are read, and then the read data should be again stored in the device in outside of the chip. Accordingly, the non-volatile memory device having the MLC should use algorithm for the copyback operation different from algorithm in the non-volatile memory device having the SLC.
On the other hand, in case that data of a source page are damaged during the copyback operation, the damaged data should be amended.
Additionally, an LSB program operation and an MSB program operation are performed in accordance with the copyback operation of the MLC. Here, since a verifying operation is performed about each of the program operations, unified verifying operation has been required.